Glass fibres can be produced by melting a glass composition in a melter and drawing them out through the tip plate of a bushing assembly. A bushing assembly is generally in the form of a rectangular box with two pairs of opposite side and end walls forming the perimeter thereof with an opening at the top in fluid communication with the melter. The bottom floor comprises a tip plate which is a plate comprising a multitude of orifices or tips through which the glass melt can flow to form fibres, which are attenuated to reach their desired diameter. To ensure an optimal control of the glass composition and viscosity, the molten glass must be well homogenized and the temperature of the tip plate must be controlled accurately. The temperature of the tip plate depends on the glass melt composition but is generally well above 1000° C. Because of the extreme working conditions, the various components of a bushing assembly are made of platinum or platinum alloys, typically rhodium-platinum alloys. The amounts of such expensive alloys used in the manufacturing of bushing assemblies is therefore of economical concern, even though most of the material can be recycled, since a larger material pool is required at the premises of the bushing manufacturer to ensure a continuous supply of bushing assemblies.
The load applied on the tip plate is substantial with, on the one hand, the weight of the glass melt lying on top of it and, on the other hand, the drawing force applied to the fibres below. At temperatures well above 1000° C., it is not surprising that tip plates are sensitive to creep and sagging. In order to increase the production rate, larger tip plates are being used which increase the problem of creep and sagging. For this reason, beside the use of transverse gussets distributed along the length of the tip plate, a longitudinal central stiffening rib is often provided in the centre of the floor to stiffen the tip plate in the longitudinal direction; this configuration corresponds to having two tip plates in parallel separated by a longitudinal beam in a single bushing assembly. Usually, the two tip plate portions and the central beam are made of a single plate folded appropriately. The central beam may, however, be welded to the centre of the top surface of a single tip plate or to the longitudinal edges of two separate tip plates. Examples of bushing assemblies comprising a central stiffening rib, dividing the floor of the bushing assembly into two tip plates are disclosed in WO2000/001630, WO2009/128749, WO9958460, or EP0931026.
The homogeneity of the glass melt composition and temperature can be improved before it reaches the tip plate(s) by splitting the flow by interposing baffles and perforated screens in the flow path. U.S. Pat. No. 5,928,402 discloses a multi-screen mixing apparatus for a bushing assembly including a first, upstream screen having openings located at a first portion thereof through which the glass melt must flow and a second, downstream screen having openings located at a second portion thereof offset with respect to the first portion of the upstream screen, such that the molten glass must flow in a non-linear path as it passes through the screens. WO2000/001630 discloses a glass fibre production assembly comprising multiple perforated screens arranged along the flowpath of molten glass from the furnace down to the tip plate, with a diverter (44) arranged just above the bushing assembly and tip plates separated by a central rib. Similarly, WO2009/128749 discloses a glass fibre production assembly with multiple screens laid on the flow path of molten glass from a source of molten glass to two tip plates separated by a central stiffening rib. WO200811298 discloses a tip plate being separated from a source of molten glass by a zigzagging screen and EP1509478 by a flat screen. US20071220923 discloses a flow diverter (340) from a furnace and a bushing assembly. U.S. Pat. No. 4,525,188 discloses a bushing assembly wherein molten glass is fed to the tip plates through a plurality of tubular feed inlets through a top cover chamber. U.S. Pat. No. 4,537,609 discloses a bushing assembly provided with a baffle assembly separating a source of molten glass from the tip plate. In all the foregoing bushing assemblies, the features for stiffening the tip plate(s) are distinct from the ones used for homogenizing the glass melt, which results in the use of higher amounts of expensive alloys. EP0931026 discloses a bushing assembly wherein the tip plate is reinforced by a series of adjacent and perforated A-shaped ribs. In this configuration the A-shaped ribs ensure both functions of stiffening the tip plate and splitting the molten glass flow to homogenize the composition and temperature thereof.
The present invention provides a new design for bushing assemblies, allowing an efficient reinforcement of the tip plates and excellent homogenization of the molten glass while reducing the amount of expensive alloys used for its manufacturing. This and other advantages of the present invention are presented in continuation.